Architecture for providing cellular roaming support

ABSTRACT

A network may include an International Serials Data System (ISDS) that is configured to register and determine an identity of a receiving or originating user equipment (UE) that has a home network that operates using a different format or standard than the current network. The ISDS may be configured to generate transmissions on behalf of the UE for registration and identification for outgoing and incoming voice or text messages using the format of both networks.

BACKGROUND

Today, many networks provide roaming support to each other to enhanceand increase a serviceable area for their network users. However, asnetwork technologies have advanced some networks have lagged behind orfailed to implement the newest network technologies. This growing dividebetween networks has resulted in some incompatibilities between networksthat typically offer roaming support to each other's users. For example,many networks still rely on circuit switched (CS) systems while the moreadvanced systems have been upgraded to provided Voice over Long-TermEvolution (VoLTE) systems. Thus, an architecture for the VoLTE networksto provide roaming support for CS network users is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items or features.

FIG. 1 is an example of a block diagram of a network equipped with anInternational Switched Digital Service configured to host vesting UEsassociated with a CS-based home network, in accordance with someexamples of the present disclosure.

FIG. 2 is an example flow diagram showing an illustrative processassociated with hosting a visiting CS-based user equipment on a VoLTEbased visited public land mobile network, in accordance with someexamples of the present disclosure.

FIG. 3 is an example flow diagram showing an illustrative processassociated with hosting a visiting CS-based user equipment on a VoLTEbased visited public land mobile network, in accordance with someexamples of the present disclosure.

FIG. 4 is an example of a data flow diagram for registering a VoLTE userequipment to a CS network, in accordance with some examples of thepresent disclosure.

FIG. 5 is an example of a data flow diagram associated with routing amobile originating call from a visiting user equipment over a visitedpublic land mobile network, in accordance with some examples of thepresent disclosure.

FIG. 6 is an example of a data flow diagram associated with routing amobile terminating call for a visiting user equipment over a visitedpublic land mobile network, in accordance with some examples of thepresent disclosure.

FIG. 7 is an example of a data flow diagram associated with routing amobile originating short-message-service from a visiting user equipmentover a visited public land mobile network, in accordance with someexamples of the present disclosure.

FIG. 8 is an example of a data flow diagram associated with routing amobile terminating short-message-service from a visiting user equipmentover a visited public land mobile network, in accordance with someexamples of the present disclosure.

FIG. 9 is another example of a data flow diagram associated with routinga mobile originating short-message-service from a visiting userequipment over a visited public land mobile network, in accordance withsome examples of the present disclosure.

FIG. 10 is another example of a data flow diagram associated withrouting a mobile terminating short-message-service from a visiting userequipment over a visited public land mobile network, in accordance withsome examples of the present disclosure.

DETAILED DESCRIPTION

Discussed herein are systems, architectures, and methods associated withVoLTE networks to provide registration, voice calling, text-message, andthe like for roaming users that are currently associated with a CSnetwork. For instance, many networks support roaming services for eachother's users to enhance and increase a serviceable area associated withthe individual networks. In some cases, a roaming partner's network maystill rely on CS (or other legacy standards) based user equipment (UE)that may not be supported on more up-to-date VoLTE UEs. As such, thesystem, discussed herein, may be configured to register roaming VoLTEUEs to CS networks as a roaming user without maintaining dedicated CSnetwork resources on the UE.

In some cases, the system may be configured to route mobile originating(MO) and mobile terminating (MT) calls, short message service (SMS)text-based messages, and the like between the VoLTE UEs roaming on theCS network with other UEs, as discussed below. In some cases, the CSnetwork may act as a visited public land mobile network (VPLMN) toregister, process calls and messages, and authenticate the roaming orvisiting UE via a home location register (HLR) of a corresponding VoLTEhome public land mobile network (HPLMN). A VPLMN is a public land mobilenetwork that a user or UE may access as a visiting or roaming devicewhen leaving the HPLMN associated with the user and/or UE.

In one implementation, the VPLMN may be configured with an InternationalSwitched Digital Service (ISDS) that is capable of receiving andtransmitting requests from components of the VPLMN network on behalf ofUEs located within a service area of the VPLMN using a first protocol,such as 4G, 5G, VoLTE and the like. The ISDS may also be configured totransmit and receive requests using various legacy protocols (e.g., CSnetwork based requests) when registering visiting UEs, placing incomingor outgoing calls, and/or placing incoming or outgoing SMS messages. Inthis manner, the ISDS may be equipped with components to translate orotherwise process requests using multiple standards and/or protocols.

FIG. 1 is an example 100 of a block diagram of a network 102 equippedwith an ISDS 104 configured to host visiting UEs 106 associated with aCS-based home network 108, in accordance with some examples of thepresent disclosure. In some cases, the ISDS 104 may be configured toreceive and transmit requests associated with the visiting UE 108 usingthe VoLTE standard. For example, the VoLTE-based transmissions 110(e.g., confirmations, data, and requests) may include a registrationrequest, an authentication request, a multimedia authentication request,registration confirmations, authentication confirmations, and the like.In some cases, the VoLTE standard transmissions 110 may be received fromand sent to other components of the VPLMN 102, such as anIntegrating-Call Session Control Function, Proxy-Call Session ControlFunction, a Serving-Call Session Control Function, and the like.

The ISDS 104 may also be configured to transmit and receive CS-basedtransmissions 112 (e.g., confirmations, data, and requests) from theHPLMN 108 associated with the visiting UE 106. For example, the ISDS 104may be configured to translate or convert the VoLTE-based transmissions110 into a CS-based transmissions 112 prior to transmitting tocomponents of the HPLMN 108. The ISDS 104 may also be configured totranslate or convert the CS-based transmissions 112 into a VoLTE-basedtransmissions 110 prior to transmitting to components of the VPLMN 102.For instance, as an illustrative example, the ISDS 104 may receive aVoLTE Multimedia Authentication Request and in response send a CSauthentication information request to the HPLMN 108 to obtain, forinstance, subscriber data associated with the visiting UE 106. In thisexample, the ISDS 104 may convert the subscriber data from the CS formatinto a VoLTE format to complete, for instance, a registration of thevisiting UE 106 by other components of the VPLMN 102.

FIGS. 2 and 3 are flow diagrams illustrating example processesassociated with hosting visiting CS-based UEs on a VoLTE based networkaccording to some implementations. The processes are illustrated as acollection of blocks in a logical flow diagram, which represent asequence of operations, some or all of which can be implemented inhardware, software, or a combination thereof. In the context ofsoftware, the blocks represent computer-executable instructions storedon one or more computer-readable media that, which when executed by oneor more processors, perform the recited operations. Generally,computer-executable instructions include routines, programs, objects,components, encryption, deciphering, compressing, recording, datastructures and the like that perform particular functions or implementparticular abstract data types.

The order in which the operations are described should not be construedas a limitation. Any number of the described blocks can be combined inany order and/or in parallel to implement the process, or alternativeprocesses, and not all of the blocks need be executed. For discussionpurposes, the processes herein are described with reference to theframeworks, architectures and environments described in the examplesherein, although the processes may be implemented in a wide variety ofother frameworks, architectures or environments.

FIG. 2 is an example flow diagram showing an illustrative process 200associated with hosting a visiting CS-based user equipment on a VoLTEbased VPLMN network, in accordance with some examples of the presentdisclosure. In some cases, a CS-based UE may attempt to register withthe VoLTE based VPLMN and/or send a mobile originating call or text withrespect to another UE.

At 202, an ISDS of the VPLMN may receive a first VoLTE transmissionassociated with the visiting CS-based UE. For example, the first VoLTEtransmission may be a registration request, a Multimedia AuthenticationRequest, an INVITE message, an SMS message, or the like. In theseexamples, the ISDS may obtain information associated with the CS-basedUE from the home network of the CS-based UE (e.g., the CS-based UE'sHPLMN).

At 204, the ISDS may generate a first CS transmission based at least inpart on the first VoLTE transmission. For example, the ISDS may convertthe CS transmission from a first format associated with the VPLMN to asecond format associated with the HPLMN of the CS-based UE. In thismanner, the VPLMN may operate using the first format while the ISDS isable to obtain information and data associated with the CS-based UE fromthe HPLMN using the second format.

At 206, the ISDS may send the first CS transmission to the HPLMN. Forexample, the first CS transmission may be an authorization informationrequest, a location data request, an INVITE message, a mobileoriginating-forward short message (MO-FSM), and the like.

At 208, the ISDS may receive from the HPLMN a second CS transmissionassociated with the visiting CS-based UE. For example, the second CStransmission may be a location response, a mobile subscriber data orinformation, AKA vectors, INVITE response, MO-FSM response, and thelike.

At 210, the ISDS may generate a second VoLTE transmission based at leastin part on the second CS transmission. For example, the ISDS may convertor otherwise generate a second VoLTE transmission using data associatedwith the second CS based transmission. For example, an Inter-WorkingFunction (IWF) associated with the ISDS 122 may build and/or storerelevant profile information or data associated with the CS-based UE 102received as mobile subscriber data from the HPLMN.

At 212, the ISDS may send the second VoLTE transmission to anothercomponent of the VPLMN and, at 214, the other component may perform anoperation associated with the CS-based UE. In some cases, the othercomponents may include an Integrating-Call Session Control Function, aServing-Call Session Control Function, a Proxy-Call Session ControlFunction, and the like. For example, the Serving-Call Session ControlFunction may assign network resources (such as a server) to the CS-basedUE in response to receiving the second VoLTE transmission.

FIG. 3 is an example flow diagram showing an illustrative processassociated with hosting a visiting CS-based user equipment on a VoLTEbased visited public land mobile network, in accordance with someexamples of the present disclosure. In some cases, a CS-based UE mayreceive a mobile terminating call or text with respect to another UE.

At 302, an ISDS of the VPLMN may receive a first CS transmissionassociated with the visiting CS-based UE. For example, the first CStransmission may be a send routing information request, an Identity andAccess Management Request, or the like. In these examples, the first CStransmission may be associated with a mobile terminating call or textmessage.

At 304, the ISDS may generate a first VoLTE transmission based at leastin part on the first CS transmission. For example, the ISDS may convertthe first VoLTE transmission from a first format associated with theHPLMN to a second format associated with the VPLMN. In this manner, theVPLMN may operate using the second format while the ISDS is able toobtain information and data associated with the CS-based UE from theHPLMN using the first format.

At 306, the ISDS may send the first VoLTE transmission to a component ofthe VPLMN. For example, the first VoLTE transmission may be a MobileTerminating Forward short message that the ISDS may convert to a VoLTESIP message for forwarding to the visiting UE via, for example,Serving-Call Session Control Function and/or a Proxy-Call SessionControl Function.

At 308, the ISDS may receive from the component of the VPLMN a secondVoLTE transmission associated with the visiting CS-based UE. Forexample, the second VoLTE transmission may be an acknowledgement of thetext message or the like.

At 210, the ISDS may generate a second CS transmission based at least inpart on the second VoLTE transmission. For example, the ISDS may convertor otherwise generate a second CS transmission using data associatedwith the second VoLTE transmission. The second VoLTE transmission maythen be sent or otherwise provided to the HPLMN associated with thevisiting UE.

FIG. 4 is an example of a data flow diagram for registering a CS userequipment 402 to a VoLTE network, in accordance with some examples ofthe present disclosure. For example, the UE 406 may be associated with aCS-based HPLMN 404 but may be attempting to register as a roaming orvisiting device on a VoLTE-based VPLMN 406. In other words, the UE 402may be at a location that is outside of the network coverage provided bythe HPLMN 404 but within the network coverage area of the VPLMN 406.

Initially, at 408, the UE 402 may discover a Proxy-Call Session ControlFunction (P-CSCF) 410 associated with the VPLMN 406. The UE 402 may thentransmit or send a registration request 412 to the detected P-CSCF 410.The P-CSCF 410 may act as a first point of contact between the UE 402and the VPLMN 406. The registration request 412 may include a UniformResource Identifier (URI) associated with the UE 402 to assist theP-CSCF 410 in processing the registration request.

At 414, the P-CSCF 410 may select an Integrating-Call Session ControlFunction (I-CSCF) 416 for the UE 402 based on a home domain indicated bythe URI in the registration request 412. For example, the P-CSCF 410 mayselect a Mobile Network Code (MNC), a Mobile Country Code (MCC), orother identifiers for the HPLMN 404 associated with UE's 402. In somecases, the P-CSCF 410 may configure an associated Domain Name Server(DNS) to return an address associated with the I-CSCF 416 to avoidchanges to a Unified Access Gateway (UAG) associated with the UE 402.The I-CSCF 416 may assist with routing requests to an appropriateservice function, such as Serving-Call Session Control Function (S-CSCF)426 discussed below.

At 418, the I-CSCF 416 selected by the P-CSCF 410 may receive theregistration request 408 or an indication of the registration request412. The I-CSCF 416 may select a Home Subscribers Server (HSS) for theUE 402 based on the MNC and/or MCC associated with the HPLMN 404. Inother examples, the I-CSCF 416 may select the HSS for the UE 402 basedon an Internet protocol multimedia private identity (IMPI/IMPU) and/or adomain name indicated by the URI associated with the UE 402. The I-CSCF416 may then generate and forward a unified authentication request (UAR)420 associated with the UE 402 to an International Switched DigitalService (ISDS) 422.

At 424, the ISDS 422 may check to determine if the UE 402 is anauthorized roaming partner device and confirm or determine if the S-CSCF426 for the UE 402 is assigned. If the UE 402 passes the roaming partnercheck and the S-CSCF 426 is assigned, the ISDS 422 may return a UnifiedAuthentication Accept (UAA) message 428 to the I-CSCF 416. The I-CSCF416 may also send or forward the registration request 412 or anindication of the registration request 412 to the assigned S-CSCF 426,which in response sends a Multimedia Authentication Request (MAR) 430 tothe ISDS 422.

At 432, the ISDS 422 may initiate an authentication process with theHPLMN 404. For example, the ISDS 422 may send authentication information434 to a Home Location Register (HLR) 436 associated with the HPLMN 404.As discussed above, the ISDS 422 may receive the MAR 430 as a VoLTEbased transmission and send the authentication information 434 as aCS-based transmission compatible or readable by the HLR 436 of the HPLMN404. The HLR 436 may be a database that contains or stores various dataabout mobile subscribers of a mobile network, such as the mobilenumbers, services and whether a number has been ported to anothernetwork, and the like.

The HLR 436 may return also known as (AKA) vectors 438 for the UE 402 tothe ISDS 422. Again, the AKA vectors 438 may be transmitted as aCS-based transmission that is received and processed by the ISDS 422.The ISDS 422 may then send updated location data 440 associated with theUE 402 to the HLR 436 of the HPLMN 404 as another CS-based transmission.In some cases, the ISDS 422 and the HLR 436 may also exchange subscriberdata (SD) via a CS-based message 442 and a CS response 444. The HLR 436may also return a CS-based confirmation or response 446 associated withor acknowledging the updated location data 440. In one example, the ISDS422 may translate a diameter of the CS-based message to a diameterassociated with a media access plan or protocol (MAP) readable by theVPLMN 406. The ISDS 422 may also forward the MAP to the HLR 436 andstore the user profile or UE profile data.

At 448, an Inter-Working Function (IWF) associated with the ISDS 422 maybuild and/or store relevant profile information or data associated withthe UE 402 in a format associated with the VPLMN 406 and received fromthe HLR 436 of the HPLMN 404. The S-CSCF 426 may then return either anunauthorized message and/or the aka vectors information 438 to the UE402, the I-CSCF 416, and/or the P-CSCF 410, as illustrated.

At 450, the UE 402 may send a message (such as UAR 452) to the ISDS 422.The ISDS 422 may, in response, provide a server-name 462 to the I-CSCF416, with which the ISDS 422 may complete the registration process withthe VPLMN 406, as shown. For example, at 454, if the authentication issuccessful, the S-CSCF 426 provides a Server-Assignment-Request (SAR)456 to the ISDS 422 and a Server-Assignment-Answer (SAA) 458 is returnedby the ISDS 122. Upon receipt of the SAA 458, the S-CSCF 426 may send aconfirmation 460 of the registration back to the UE 402.

At 462, the S-CSCF 426 may execute an iFC process and the UE 402 may beregistered with a Telephone Application Server (TAS) 464 associated withthe VPLMN 406. In some cases, at 466, the TAS 464 may select a HomeSubscriber Server (HSS) for the UE 402 based on the MCC, MNC, the IMPI,the IMPU, the domain name indicated by the URI associated with the UE402, a combination thereof, or the like. The TAS 464 may then send adiameter associate with a Sub network router (Sh-SNR) 468 to the ISDS422. In response, the ISDS 422 may provide a diameter associated withthe Systems Network Architecture (SNA) 470 to the TAS 464. The TAS 464may then send an OK or approval message 472 to the S-CSCF 126. TheS-CSCF 426 may then register the UE 402 with an Interface MessageProcessor (IMP) 474.

At 476, the IMP 474 may query a contract data requirement list (CRDL) todetermine if a Uniform Network Resource Identifier (UNRI) is set orotherwise configured for the UE 402. In some cases, the TAS 474 may alsowrite or store registering data. Once, the CRDL configuration isconfirmed, the TAS 464 may return an OK or approval message 478 to theS-CSCF 426 and the UE 402 is fully registered with the VPLMN 406.

FIG. 5 is an example of a data flow diagram 500 associated with routinga mobile originating call (MOC) from a visiting UE 502 over a VPLMN 504,in accordance with some examples of the present disclosure. Initially,the VPLMN 504 receives an inbound MOC from a UE 502. The inbound MOC maybe routed in a similar manner as to the VoLTE calls. The MOC may bereceived at a P-CSCF 506 in the form of an INVITE message 508. TheP-CSCF 506 may forward the INVITE message 508 to a S-CSCF 510 and theS-CSCF 510 may execute the iFC process. The INVITE message 508 may thenbe received by a TAS 512. The TAS 512 may execute the originatingservices and the S-CSCF 510 may route the call to a mobile terminating(MT) UE (not shown) in a traditional manner.

FIG. 6 is an example of a data flow diagram 600 associated with routinga mobile terminating call (MTC) for a visiting UE 602 over a VPLMN 604,in accordance with some examples of the present disclosure. Initially, aGateway Mobile Switching Center (GMSC) 606 associated with a HPLMN 608sends a send routing information (SRI) request 608 to a HLR 612 of theHPLMN 608. In response, the HLR 612 sends a Mobile Subscriber IntegratedServices Digital Network Number (MSISDN) 614 to an ISDS 642 associatedwith the VPLMN 604.

At 616, the ISDS 642 may allocate, store, and/or check a Mobile StationRoaming Number (MSRN) against the MSISDN 614 received from the HLR 612.If the ISDS 642 identifies a match, the ISDS 642 may return a MSRN 618to the HLR 612 associated with the HPLMN 608 and the HLR 612 may send anSRI response 620 to the GMSC 606. In this example, the MSISDN 614 andthe MSRN 618 may be sent and received in a first format (e.g., a CSbased transmission) associated with the HPLMN 608.

At 622, the GMSC 606 may generate an Identity and Access Management(IAM) MSRN request 624 and forward to a Media Gateway ControllerFunction (MGCF) 626 associated with the VPLMN 604. The MGCF 626 maytranslate the IAM MSRN request 624 to an INVITE message 628. The INVITEmessage 628 is provided to a I-CSCF 630 associated with the VPLMN 604.

At 632, the I-CSCF 630 may select an IWF for use with the MTC and send aLocal Internet Registry (LIR) request 640 (640 is used twice as LIRrequest and TAS, here and in the PDF) to the ISDS 642. The LIR request640 may be in a second format (e.g., a VoLTE based format) associatedwith the VPLMN 604. At 634, the LIR request 640 indicates the MSRN 618,and the IWF determines the MSISDN 614 associated with the MRSN 618,returns a custom AVP, and assigns a S-CSCF 636 to the MOC. The ServerName associated with the S-CSCF 636 and the MSISDN 614 are then sent tothe I-CSCF 630 which sends an INVITE 638 to the S-CSCF 636, therebyrouting the MTC to the S-CSCF 636. The INVITE 638 may indicate theMSISDN 614. The S-CSCF 636 may apply initial filter criteria to routethe MTC to a TAS 644. The TAS 644 may then perform terminating servicesand route the MTC to the UE 602 via a corresponding P-CSCF 642, asshown.

FIG. 7 is an example of a data flow diagram 700 associated with routinga mobile originating short-message-service (SMS) from a visiting UE 702over a VPLMN 704, in accordance with some examples of the presentdisclosure. In the illustrated example, the UE 702 may send a message706 to the P-CSCF 708 of the VPLMN 704. The message 706 may include aSMS-SUBMIT request (in a first format associated with the VPLMN 704) andinclude a R-URI, an indication of a HPLMN 710 associated with the SMSmessage, a SMS control address, and the like. The P-CSCF 708 may forwardthe message 706 to a S-CSCF 412. The S-CSCF 712 may execute an iFCprocess and send the message to an ISDS 714 in the first formatassociated with the VPLMN 704, as illustrated. The ISDS 714 may thenconvert the message 706 to a second format associated with the HPLMN710. For example, the first format may be a VoLTE based transmissionformat and the second format may be a CS based transmission format. TheISDS 714 may then send a CS based MO-FSM 722 to the SMSC 718 of theHPLMN 710.

The ISDS 714 may receive a CS based MO-FSM response 716 (e.g., in thesecond format) from the HPLMN 710. For example, the SMSC 718 may returna CS based MO-FSM response 716 indicating a successful delivery of theSMS message. The ISDS 714 may then convert the CS based MO-FSM response716 to a VoLTE SMS submit report 720 (e.g., in the first format). TheISDS 714 may then return SMS submit report 720 to the UE 702 via theS-CSCF 712 and/or the P-CSCF 708, as shown. Finally, the UE 702 may thenacknowledge the report with the ISDS 714.

FIG. 8 is an example of a data flow diagram 800 associated with routinga MT SMS from a visiting UE 802 over a VPLMN 804, in accordance withsome examples of the present disclosure. In the currently illustratedexample, an SMSC 806 of a HPLMN 808 originating the SMS message maytransmit a send-routing information for a short message (SRI-SM) 810 toan HLR 812 associated with the HPLMN 808. The HLR 812 may then return aSRI-SM response 814 to the SMSC 806. The SRI-SM response 814 including avisitor location register (VLR) of the UE 802.

The SMSC 806 may then transmit a Mobile Terminating Forward shortmessage (MT-FSM) 816 to an ISDS 818 associated with the VPLMN 804currently servicing the UE 802. The MT-FSM 816 may be in a first format,such as a CS based transmission format associated with the HPLMN 810.The ISDS 818 may convert the MT-FSM 816 to a SIP MESSAGE in a secondformat then deliver the SIP MESSAGE 818 to the UE 802 via a S-CSCF 820and a P-CSCF 822, as shown. The second format may be a VoLTE basedtransmission format and associated with the VPLMN 804. In some cases,the UE 802 may acknowledge a receipt of the SIP MESSAGE 818 by sendingan OK response to the ISDS 818. The UE 802 may also send a MESSAGE witha delivery report 824 to the S-CSCF 820. The S-CSCF 820 may report backto the SMSC 806 via the ISDS 818, as illustrated.

Again, as discussed above, the communication with the components of theHPLMN 810 may be in the first format associated with the HPLMN 810(e.g., a CS based transmission format) and the communication within theVPLMN 804 may be in the second format (e.g., a VoLTE based transmissionformat). In this example, the ISDS 818 is responsible for converting orgenerating transmissions, request, reports, and the like in theappropriate format for each of the components. In this manner, the ISDS818 acts to translate the transmissions to a diameter or standardassociated with the responsible network 804 or 810.

FIG. 9 is another example of a data flow diagram 900 associated withrouting a MO SMS from a visiting UE 902 over a VLPMN 904, in accordancewith some examples of the present disclosure. In this example, the UE902 may initiate an SMS message using a Standard Global Service (SGs).For instance, the UE 902 may send via an uplink (UL) Non-Access Stratum(NAS) transport 906 to a mobility management entity (MME) 908 associatedwith the VPLMN 904. The transport 906 may include the SMS data. The MME908 may translate data associated with the UL NAS transport 906 to ULUnitdata 910. The UL Unitdata 910 is transmitted to an ISDS 912associated with the VPLMN 904. The ISDS 912 may also send anacknowledgment associated with the MO-FSM 914 back to the MME 908 as adownlink Unitdata 922 and the MME 908 may forward to the UE 902 via a DLNAS transport 924.

The ISDS 912 converts the UL Unitdata 910 from a first format associatedwith the VPLMN 904 to a MO-FSM 914 in a second format associated withthe HPLMN 918 and sends to SMSC 916 associated with an HPLMN 618. Forexample, the first format may be a VoLTE format and the second formatmay be a CS format. The SMSC 916 may process the MO-FSM 914 and transmita MO-FSM response 920 back to the ISDS 912. The ISDS 912 may convert theMO-FSM response 920 to a DL Unitdata 926 and sends the DL Unitdata 926to the MME 908 over the SGs. The MME 908 then converts the DL Unitdata926 to a DL NAS transport 930 and send the DL NAS transport 930 to theUE 902. In some cases, the UE 902 may provide a UL NAS transport 932back to the MME 908 acknowledging receipt of the DL NAS transport 930.

FIG. 10 is another example of a data flow diagram 1000 associated withrouting a MT SMS from a visiting UE 1002 over a VLPMN 1004, inaccordance with some examples of the present disclosure. In thisexample, the UE 1002 may receive an SMS message using a SGs. In thisexample, an SMSC 1006 of a HPLMN 1008 originating the SMS message maytransmit a SRI-SM 1010 to an HLR 1012 associated with the HPLMN 1008.The HLR 1012 may then return a SRI-SM response 1014 to the SMSC 1006 theSRI-SM response 1014 including a visitor location register (VLR) of theUE 1002.

The SMSC 1006 may then transmit a MT-FSM 1016 to an ISDS 1018 associatedwith the VPLMN 1004 currently servicing the UE 1002. The ISDS 1018 mayconvert the MT-FSM 1016 in a format associated with the HPLMN 1008 to aDL Unitdata 1038 in a format associated with the VPLMN 1004. The DLUnitdata 1038 may then be provided to the UE 1002 via an MME 1020. TheMME 1020 may initiate a service request 1022 to cause the ISDS 1018 toprovide DL Unitdata 1024. The MME 1020 may then convert the DL Unitdata1024 to a DL NAS transport 1026 which is transmitted to the UE 1002.

The UE 1002 may then initiate a delivery report 1040 to provide back tothe SMSC 1006 of the HPLMN 1008. The MME 1020 may convert the UL NAStransport 1028 to a UL Unitdata 1030 which is provided to the ISDS 1018.The ISDS 1018 may then cover the UL Unitdata 1030 to a MT-FSM response1032. The MS-FSM response 1032 is then sent to the SMSC 1006. The ISDS1018 may also respond to the UE 1002 with a final acknowledgementmessage that may be provided via the MME 1020 as DL Unitdata 1034 and DLNAS transport 1036, as illustrated.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as exemplary forms ofimplementing the claims.

What is claimed is:
 1. A computer-implemented method comprising:receiving at a proxy-call session control function (P-CSCF) of avisiting network, a registration request from a user equipment (UE);sending the registration request to interrogating call session controlfunction (I-CSCF) and a serving-call session control function (S-CSCF);generating, at the I-CSCF, a user authentication request, the userauthentication request in a first format assorted with the visitingnetwork; sending the user authorization request to an internationalserials data system (ISDS); sending, from the ISDS, a userauthentication answer to the I-CSCF, the user authentication answer inthe first format; sending, from the ISDS, authentication data to a homelocation register (HLR), the authentication data in a second formatassociated with a home network of the UE; receiving, at the ISDS,location data from the HLR, the location data in the second format;sending, from the S-CSCF, a subscriber authentication request to theISDS, the subscriber authentication request in the first format;sending, from the ISDS, a subscriber authentication answer to theC-CSCF, the subscriber authentication answer in the first format; andregistering the UE with an IP Multimedia Subsystem (IMS).
 2. Thecomputer-implemented method as claim 1 recites, further comprising:sending, from the S-CSCF, the registration request to a mobile telephoneapplication server; and receiving, at the S-CSCF and from the mobiletelephone application server, authorization to register the UE prior toregistering the UE with the IMS.
 3. The computer-implemented method asclaim 1 recites, wherein the mobile telephone application server sends adiameter associated with a sub-network router to the S-CSCF prior toregistering the UE with the IMS.
 4. The computer-implemented method asclaim 1 recites, further comprising receiving, at the ISDS, subscriberdata associated with the UE from the HRL in response to sending theauthentication data, the subscriber data in the second format.
 5. Thecomputer-implemented method as claim 1 recites, further comprising:receiving, at the S-CSCF, a short message short message service (SMS)message from the UE; forwarding the SMS message to the ISDS; sending,from the ISDS to a short message service center (SMSC), a mobileoriginating-forward short message (MO-FSM), the MO-FSM in the secondformat; receiving, at the ISDS, a response from the SMSC, the responsein the second format; and sending to the UE, from the ISDS, a SMS-submitreport.
 6. The computer-implemented method as claim 1 recites, furthercomprising: generating, at the S-CSCF, a multimedia authenticationrequest, the multimedia authentication request in the first format;sending the multimedia authentication request to the ISDS; and sending,from the ISDS, a multimedia authentication answer to the S-CSCF, themultimedia authentication answer in the first format.
 7. Thecomputer-implemented method as claim 1 recites, further comprisingdetermining by the ISDS that the UE is an authorized roaming partnerdevice prior to sending the user authentication answer to the I-CSCF. 8.The computer-implemented method as claim 1 recites, further comprisingreceiving, at the ISDS, also-known-as vectors from the HLR, thealso-known-as vectors in the second format.
 9. A system comprising: oneor more processors; a memory communicatively coupled to the one or moreprocessors, the memory storing computer-readable instructions that, whenexecuted by the one or more processors, cause the one or more processorsto perform operations comprising: receiving at a proxy-call sessioncontrol function (P-CSCF) of a visiting network, a registration requestfrom a user equipment (UE); sending the registration request tointerrogating call session control function (I-CSCF) and a serving-callsession control function (S-CSCF); generating, at the I-CSCF, a userauthentication request, the user authentication request in a firstformat assorted with the visiting network; sending the userauthorization request to an international serials data system (ISDS);sending, from the ISDS, a user authentication answer to the I-CSCF, theuser authentication answer in the first format; sending, from the ISDS,authentication data to a home location register (HLR), theauthentication data in a second format associated with a home network ofthe UE; receiving, at the ISDS, location data from the HLR, the locationdata in the second format; sending, from the S-CSCF, a subscriberauthentication request to the ISDS, the subscriber authenticationrequest in the first format; sending, from the ISDS, a subscriberauthentication answer to the C-CSCF, the subscriber authenticationanswer in the first format; and registering the UE with an IP MultimediaSubsystem (IMS).
 10. The system of claim 9, wherein the operationsfurther comprise: sending, from the S-CSCF, the registration request toa mobile telephone application server; and receiving, at the S-CSCF andfrom the mobile telephone application server, authorization to registerthe UE prior to registering the UE with the IMS.
 11. The system of claim9, wherein the mobile telephone application server sends a diameterassociated with a sub-network router to the S-CSCF prior to registeringthe UE with the IMS.
 12. The system of claim 9, wherein the operationsfurther comprise: receiving, at the ISDS, subscriber data associatedwith the UE from the HRL in response to sending the authentication data,the subscriber data in the second format.
 13. The system of claim 9,wherein the operations further comprise: receiving, at the S-CSCF, ashort message short message service (SMS) message from the UE;forwarding the SMS message to the ISDS; sending, from the ISDS to ashort message service center (SMSC), a mobile originating-forward shortmessage (MO-FSM), the MO-FSM in the second format; receiving, at theISDS, a response from the SMSC, the response in the second format; andsending to the UE, from the ISDS, a SMS-submit report.
 14. The system ofclaim 9, wherein the operations further comprise: generating, at theS-CSCF, a multimedia authentication request, the multimediaauthentication request in the first format; sending the multimediaauthentication request to the ISDS; and sending, from the ISDS, amultimedia authentication answer to the S-CSCF, the multimediaauthentication answer in the first format.
 15. The system of claim 9,wherein the operations further comprise: determining by the ISDS thatthe UE is an authorized roaming partner device prior to sending the userauthentication answer to the I-CSCF.
 16. The system of claim 9, whereinthe operations further comprise: receiving, at the ISDS, also-known-asvectors from the HLR, the also-known-as vectors in the second format.17. One or more non-transitory computer-readable memory storingcomputer-readable instructions that, when executed by one or moreprocessors, cause the one or more processors to perform operationscomprising: receiving at a proxy-call session control function (P-CSCF)of a visiting network, a registration request from a user equipment(UE); sending the registration request to interrogating call sessioncontrol function (I-CSCF) and a serving-call session control function(S-CSCF); generating, at the I-CSCF, a user authentication request, theuser authentication request in a first format assorted with the visitingnetwork; sending the user authorization request to an internationalserials data system (ISDS); sending, from the ISDS, a userauthentication answer to the I-CSCF, the user authentication answer inthe first format; sending, from the ISDS, authentication data to a homelocation register (HLR), the authentication data in a second formatassociated with a home network of the UE; receiving, at the ISDS,location data from the HLR, the location data in the second format;sending, from the S-CSCF, a subscriber authentication request to theISDS, the subscriber authentication request in the first format;sending, from the ISDS, a subscriber authentication answer to theC-CSCF, the subscriber authentication answer in the first format; andregistering the UE with an IP Multimedia Subsystem (IMS).
 18. The one ormore non-transitory computer-readable memory of claim 17, wherein theoperations further comprise: sending, from the S-CSCF, the registrationrequest to a mobile telephone application server; and receiving, at theS-CSCF and from the mobile telephone application server, authorizationto register the UE prior to registering the UE with the IMS.
 19. The oneor more non-transitory computer-readable memory of claim 17, wherein themobile telephone application server sends a diameter associated with asub-network router to the S-CSCF prior to registering the UE with theIMS.
 20. The one or more non-transitory computer-readable memory ofclaim 17, wherein the operations further comprise: receiving, at theS-CSCF, a short message short message service (SMS) message from the UE;forwarding the SMS message to the ISDS; sending, from the ISDS to ashort message service center (SMSC), a mobile originating-forward shortmessage (MO-FSM), the MO-FSM in the second format; receiving, at theISDS, a response from the SMSC, the response in the second format; andsending to the UE, from the ISDS, a SMS-submit report.